Stent devices are useful for holding open bodily lumens of a human or animal patient. Of particular interest to the present invention are stent devices for holding open vascular lumens, such as veins or arteries, of a human patient.
A self-expanding stent device of interest to the present invention is compacted into a reduced profile delivery configuration and mounted about an inner catheter. The stent device is made of a shape memory material and will maintain its reduced profile configuration when below a transition temperature. Once the transition temperature is breached, the stent device will tend to return to its expanded profile, deployed configuration for holding open the bodily lumen. An outer sheath is provided to maintain the stent device in the reduced profile configuration even when the transition temperature is breached until the stent device is at a target treatment site. The delivery device is threaded through the passageways of the vasculature system to arrive the stent device at the treatment site. A guide wire is used, which extends through a lumen in the inner catheter, to guide the delivery device as appropriate. At the treatment site, the outer sheath is retracted to release the stent device to expand to the deployed configuration.
Generally, the inner catheter is provided with an anchor means to axially hold the stent device to the inner catheter as the outer sheath is retracted.
One known type of anchor means is a proximal stop abutting a proximal end of a stent device, as discussed with respect to FIGS. 1 and 2 in WO 00/71058. There is friction between an outer sheath and a stent device as the outer sheath is dragged over the outer surface of the stent device during retraction for deployment. Without the proximal stop, this friction would tend to move the stent device with the outer sheath. So that the stent device can be released, the proximal stop holds the stent device axially to the inner catheter and the outer sheath moves over the stent device. With this proximal stop arrangement, the friction tends to foreshorten the stent device, which compromises deployment accuracy. Furthermore, the total force on the proximal end of the stent device could damage the structure of the stent device, particularly as longer stent devices are used.
One alternative anchor means has been disclosed in WO 00/71058 whereby a surface element is fixed to an inner catheter and arranged to engage an inner surface of the stent device. One form for the surface element is a high friction sleeve extending continuously the full length of the stent device. The high friction sleeve holds the stent device axially to the inner catheter in a manner so that the force induced between the stent device and the inner catheter by the outer sheath dragging over the stent device during deployment is evenly distributed. The engagement between the sleeve and the inner surface of the stent device also forces the stout device into the outer sheath, which increases the overall deployment force as the outer sheath more strongly drags over the stent device. The degree of deployment force will increase with radial resiliency of the sleeve pushing the stent device radially into the outer sheath.
Another alternative disclosed in WO 00/71058 is to have axially spaced radial protuberances distributed along the length of, and engaging the inner surface of, the stent device. The reduced contact area between the stunt device and the radial protuberances, as compared to a continuous sleeve, reduces the overall deployment force, while at the same time distributing the force between the inner surface of the stent device and the inner catheter.
WO 2004/096091 discloses an inner catheter disposed radially within the lumen of the stent device having a spiral wire mounted thereabout. The spiral wire provides protrusions for engaging an inner surface of the stent device to hold the stent device axially as the outer sheath is retracted axially to release the stent device.
There is still a need in the art to reduce the deployment force in retracting an outer sheath to release a stent device, particularly with longer stent devices, while at the same time ensuring deployment accuracy. One object of the present invention is to meet this need.